I called the the place that installed my riocar and they told me that the riocar is not designed to be a stand alone unit,and it would sound better If I got a second head unit and ran it thru the aux in of that unit.

This is an incorrect statement. The Rio Car is, in fact, designed to be a stand alone unit and does (in my opinion) work the best that way. This is the way I run it, and I get fantastic sound quality out of it. Many other users here on the BBS will attest to that fact.